The present invention relates to Otto-cycle internal combustion engines, and more particularly the invention relates to a system for operating the engine in such a manner that improved fuel consumption and reduced amount of NO.sub.x emissions are ensured.
In a known type of mixture-compression type Otto-cycle engine, an ignition method is used in which a high voltage of 10 to 15 KV generated from the ignition system near the Top Dead Center of the engine is applied to the proper spark plug and a basically capacitive discharge is caused between the electrodes of the spark plug, thus producing an electric spark and thereby igniting the compressed air-fuel mixture.
However, this type of prior art method, particularly a method in which a high voltage is applied periodically is disadvantageous in that if the mixture is leaned out or the amount of exhaust gas recirculation is increased greatly, the mixture will be ignited insufficiently thus tending to cause misfire, the combustion will be made unstable, the fuel consumption will still remain insufficient and the amount of NO.sub.x emissions will also be large.